This Application claims foreign priority benefits under Title 35, United States Code, Section 119 based on British Patent Application Number 9919608.1 filed in the United Kingdom on Aug. 19, 1999 and British Patent Application Number 9927366.6 filed in the United Kingdom on Nov. 20, 1999.
This invention relates to a lighting control device, and more specifically to a control device adapted for use in conjunction with arrays of white light emitting diodes, hereinafter referred to as WLEDs. In particular, the invention hereinafter described has particular application in the field of dedicated aircraft seat lighting, as WLEDs are beginning to replace the fiber optic lighting systems that are currently in widespread use.
British Patent Application No. 2317421 describes a modular aircraft seat lighting arrangement comprising a plurality of fiber optic cables, ends of which are grouped together in a so-called common end which is illuminated by a high intensity light source, the alternate ends known as fiber optic tails being used to transfer light from the light source to a plurality of different locations. The individual fiber optic cables that connect the tails and the common ends are often bulky and cumbersome, and are thus integrally disposed within or underneath the seats for which they are adapted to provide illumination.
This arrangement does represent a significant advance over the conventional aircraft seat lighting arrangement in which individual lights are incorporated in a mass-produced console unit above each passenger seat on the aircraft, because the fiber optic tails can be sheathed in a flex and stay type member and thus the occupant of a seat can move the tail to any desired position. However, the fiber optic seat-lighting arrangement has a number of disadvantages. For instance, the apparatus is bulky. When one considers that modern aircraft have seats arranged in banks of three, and a lighting arrangement is generally provided within or underneath each bank of seats, it can be appreciated that the increase in overall weight of the aircraft is significant, especially in larger aircraft that may have seating for over 400 passengers, for example.
A further disadvantage of the fiber optic lighting arrangement is its power consumption, which is relatively high on account of the requirement to power the high intensity lights that illuminate the common ends of the cables.
The recent introduction and customer acceptance of WLEDs has given rise to the development of WLED lighting systems for aircraft, as it is the current belief that WLED systems will displace fiber optic lighting arrangements from their dominant position within the field of aircraft seat lighting. However, the use of WLEDs has heretofore been impeded by their proclivity towards failure, which is generally greater than the proclivity of conventional LEDs to fail. Additionally, LEDs whether WLEDs or otherwise and being essentially diodes can fail in either short circuit or open circuit, an therefore some contingency is required to be factored into any device which depends on the correct functioning of the LEDs or WLEDs to provide light in a particular area. Furthermore, the failure probabilities of WLEDs and LEDs are much higher than the high intensity light sources currently used in the fiber optic lighting arrangements, and therefore some contingency is crucial.
The applicant has realized that a cluster arrangement of WLEDs having a plurality of WLEDs therein would provide sufficient contingency against total failure of the light because it would be very unlikely for all the WLEDs in the cluster to fail during a single use. Furthermore they have also realized that at least some of the WLEDs within the cluster must be connected in parallel because the open circuit failure of a single WLED if all were connected in series would result in total failure of the light.
The use of WLEDs has also been previously impeded by the electronic and physical sensitivity of such components. For instance, WLEDs are highly temperature and current sensitive devices, and a slight increase in the operating temperature or electric current being passed can dramatically reduce the life expectancy of the device. It should also be mentioned that diodes being semi-conductor devices have complex temperature dependent resistance, and thus voltage and current characteristics.
A further difficulty associated with the provision of uniform intensity light with WLEDs is that the voltage supplies on aircraft and within vehicles are often non-uniform. The electrical sensitivity of WLEDs and their increased likelihood of failure during the occasional power surges which may be experienced gives rise to the need for some form of compensation to ensure that the working life of the WLEDs is prolonged as much as possible.
Although the following invention is described primarily with particular reference to the lighting of individual aircraft seats, it is to be understood that the applications for embodiments of the invention are not so limited. WLED clusters can be used in any environment where illumination of a particular and discreet area is required, and where there is furthermore a requirement for user flexibility and versatility inasmuch as the lighting arrangement be capable of adopting a number of positions and orientations with respect to its mounting. Such lighting arrangements are particularly suited to providing reading lighting to the occupant of a seat.
One advantage of the present invention is that it provides a device for monitoring and controlling the operation of a lighting device including a cluster of WLEDs. The monitoring and controlling device ensures safe and uninterrupted operation of the lighting device and can compensate for changes in the operating characteristics of the cluster of WLEDs and for failure of one or more WLEDs during operation.
In one embodiment, a lighting device comprises a cluster of WLEDs, at least some of which are chained in parallel between a pair of lines that apply a voltage across the WLEDs chains. Each WLED chain has at least one WLED therein, characterized in that first current altering means and second and further current altering means are also provided between the lines, said first current altering means being capable of adjusting the total current drawn from the voltage lines by the chained WLEDs and the second and further current altering means being provided in at least one of the chains to adjust the particular current through said chain.
In one version, primary current measuring means are also provided between the voltage lines and the chains for measuring the total current being drawn by all the WLED chains.
In another version, each of the WLED chains is provided with secondary current measuring means which communicate with a control means (e.g., a microprocessor operating under the control of a computer program). The control means adjusting the current flow through the WLEDs depends, for example, on a comparison between the measured current through each WLED chain individually and, optionally, through the first current altering means.
In one implementation, three WLEDs are connected in series in each WLED chain. One advantageous configuration includes 6 chains including three WLEDs each so that the WLED cluster comprises 18 WLEDs.
In various embodiments, the current-measuring means comprises a resistor connected in series with the series-connected WLEDs in each chain and, furthermore, the first and second current altering means comprise transistors.
It is advantageous for the device to be further provided with temperature measurement means that also communicate with the control means that adjust the current flow through the WLED chains accordingly.
It is advantageous, in one or more embodiments, to provide control means that dynamically adjust the current flows through the WLED chains such that the current flow therethrough is substantially uniform and is devoid of discontinuities regardless of the operating temperature and/or the failure of one or more of the WLEDs.
In various embodiments, the control means, voltage lines, and chained series-connected WLEDs are integrated on a single circuit.
One use for which various embodiments are particularly suited is providing light for a passenger seat in an aircraft, for example. Such seats often have built-in power sources, and in such cases, it is envisioned that the device would be powered by said in-built power source.
In various embodiments, the control means also communicates with an indication means to change the state of the indication means when the control means recognizes that one or more of the WLEDs has failed. In one or more versions, an indication means comprises a light means that emits light other than white. The light means is provided in series with gate means that are also in communication with the control means between the lines. The control means activates the gate means, thus allowing current to flow through the light means to illuminate the light means only when one or more of the WLEDs has failed.
It is advantageous to mount the light means in proximity to the WLEDs so that, when a WLED has failed and the array of WLEDs is viewed, the illuminated light means is visible to the observer.
In a specific configuration, the WLEDs and the optional indication means are mounted proximate one another in hexagonal close packed arrangement on a circuit board. In such an arrangement, it is advantageous to mount the control means in the circuit board as well.
In another illustrative version, the WLEDs are connected within the circuit in groups of three WLEDs, the WLEDs of each group being connected in series as a single chain. Each three-WLED chain is connected in parallel with the other WLED chains.
It is advantageous for the grouping of the WLEDs in threes to be such that any single WLED is adjacent one other WLED with which it is connected in series. With such a configuration, the open circuit failure of any one of the WLEDs (resulting, for example, in the extinction of the remaining two WLEDs connected in series therewith in a particular chain) could be automatically compensated for without significant directional imbalance of light emission from the device.
In various embodiments, the WLEDs and optional indication means are mounted on an integrated circuit board comprising wiring and to which said control means is additionally mounted. The integrated circuit board is to be considered an independent and separately claimable aspect of this invention. Alternatively, the indication means may be provided in a remote indicator panel and directly powered from the control means. In still another alternative version, the indicator means may be simply one or more bits in a memory register that is interrogable by a suitably equipped engineer, for example.
According to a further aspect of the invention, a control means is provided for controlling current flow through a plurality of WLED chains connected in parallel between a pair of voltage lines. Each WLED chain has at least one WLED connected therein. Additionally, current altering means are connected in each chain and current measuring means are also provided in each chain that communicate with the control means, characterized in that the current flow through each of the chains is altered dependent upon a comparison effected by the control means of the current flows through each of the plurality of chains such that the said current flows are maintained substantially uniform.
In a preferred aspect, at least a single current altering means, and optionally current measurement means are provided between all of the chains and one of the voltage lines which are capable of altering and measuring respectively the total current flow through the all of the chains. In various versions, the control means also communicates with user adjustable means for increasing the intensity or dimming the light emitted from the WLEDs, and also for switching the device on and off. Preferably the control means recognizes when one or more of the WLEDs has failed and additionally causes a change of state of a further component that indicates that a fault has occurred. The further, indicating component may be, for example, a warning light which can be instantly observed, or a memory register in which a bit can be changed and stored for later analysis on connection to the control means of a lighting management system.
It will be appreciated by those skilled in the art that a device fabricated in accordance with the present invention can be controlled in a safe and reliable manner and the failures of the WLEDs used in the device can be minimized because of this operation. Furthermore, the constant and continual monitoring of the current flows through the WLED chains further mitigates against failure.
A further advantage of the device proposed herein is the uniform and relatively low power consumption throughout, for example, an aircraft which can now be achieved.